/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_dom_IDTracker_h_

#define mozilla_dom_IDTracker_h_

#include "mozilla/Attributes.h"

#include "mozilla/dom/Element.h"

#include "mozilla/dom/ShadowRoot.h"

#include "nsAtom.h"

#include "nsIDocument.h"

#include "nsThreadUtils.h"

class nsIURI;

namespace mozilla {

namespace dom {

/**

 * Class to track what element is referenced by a given ID.

 *

 * To use it, call Reset() to set it up to watch a given URI. Call get()

 * anytime to determine the referenced element (which may be null if

 * the element isn't found). When the element changes, ElementChanged

 * will be called, so subclass this class if you want to receive that

 * notification. ElementChanged runs at safe-for-script time, i.e. outside

 * of the content update. Call Unlink() if you want to stop watching

 * for changes (get() will then return null).

 *

 * By default this is a single-shot tracker --- i.e., when ElementChanged

 * fires, we will automatically stop tracking. get() will continue to return

 * the changed-to element.

 * Override IsPersistent to return true if you want to keep tracking after

 * the first change.

 */

class IDTracker {

public:

  typedef mozilla::dom::Element Element;

  IDTracker() = default;

  ~IDTracker()

  {

    Unlink();

  }

  /**

   * Find which element, if any, is referenced.

   */

  Element* get() { return mElement; }

  /**

   * Set up the reference. This can be called multiple times to

   * change which reference is being tracked, but these changes

   * do not trigger ElementChanged.

   * @param aFrom the source element for context

   * @param aURI the URI containing a hash-reference to the element

   * @param aReferrer the referrer URI for loading external resource

   * @param aReferrerPolicy the referrer policy for loading external resource

   * @param aWatch if false, then we do not set up the notifications to track

   * changes, so ElementChanged won't fire and get() will always return the same

   * value, the current element for the ID.

   * @param aReferenceImage whether the ID references image elements which are

   * subject to the document's mozSetImageElement overriding mechanism.

   */

  void Reset(nsIContent* aFrom, nsIURI* aURI, nsIURI* aReferrer,

             uint32_t aReferrerPolicy, bool aWatch = true,

             bool aReferenceImage = false);

  /**

   * A variation on Reset() to set up a reference that consists of the ID of

   * an element in the same document as aFrom.

   * @param aFrom the source element for context

   * @param aID the ID of the element

   * @param aWatch if false, then we do not set up the notifications to track

   * changes, so ElementChanged won't fire and get() will always return the same

   * value, the current element for the ID.

   */

  void ResetWithID(Element& aFrom, nsAtom* aID, bool aWatch = true);

  /**

   * Clears the reference. ElementChanged is not triggered. get() will return

   * null.

   */

  void Unlink();

  void Traverse(nsCycleCollectionTraversalCallback* aCB);

protected:

  /**

   * Override this to be notified of element changes. Don't forget

   * to call this superclass method to change mElement. This is called

   * at script-runnable time.

   */

  virtual void ElementChanged(Element* aFrom, Element* aTo)

  {

    mElement = aTo;

  }

  /**

   * Override this to convert from a single-shot notification to

   * a persistent notification.

   */

  virtual bool IsPersistent() { return false; }

  /**

   * Set ourselves up with our new document.  Note that aDocument might be

   * null.  Either aWatch must be false or aRef must be empty.

   */

  void HaveNewDocumentOrShadowRoot(DocumentOrShadowRoot*,

                                   bool aWatch,

                                   const nsString& aRef);

private:

  static bool Observe(Element* aOldElement,

                        Element* aNewElement, void* aData);

  class Notification : public nsISupports {

  public:

    virtual void SetTo(Element* aTo) = 0;

    virtual void Clear() { mTarget = nullptr; }

    virtual ~Notification() {}

  protected:

    explicit Notification(IDTracker* aTarget)

      : mTarget(aTarget)

    {

      MOZ_ASSERT(aTarget, "Must have a target");

    }

    IDTracker* mTarget;

  };

  class ChangeNotification : public mozilla::Runnable,

                             public Notification

  {

  public:

    ChangeNotification(IDTracker* aTarget,

                       Element* aFrom,

                       Element* aTo)

      : mozilla::Runnable("IDTracker::ChangeNotification")

      , Notification(aTarget)

      , mFrom(aFrom)

      , mTo(aTo)

    {}

    // We need to actually declare all of nsISupports, because

    // Notification inherits from it but doesn't declare it.

    NS_DECL_ISUPPORTS_INHERITED

    NS_IMETHOD Run() override {

      if (mTarget) {

        mTarget->mPendingNotification = nullptr;

        mTarget->ElementChanged(mFrom, mTo);

      }

      return NS_OK;

    }

    virtual void SetTo(Element* aTo) override { mTo = aTo; }

    virtual void Clear() override

    {

      Notification::Clear(); mFrom = nullptr; mTo = nullptr;

    }

  protected:

    virtual ~ChangeNotification() {}

    RefPtr<Element> mFrom;

    RefPtr<Element> mTo;

  };

  friend class ChangeNotification;

  class DocumentLoadNotification : public Notification,

                                   public nsIObserver

  {

  public:

    DocumentLoadNotification(IDTracker* aTarget, const nsString& aRef)

      : Notification(aTarget)

    {

      if (!mTarget->IsPersistent()) {

        mRef = aRef;

      }

    }

    NS_DECL_ISUPPORTS

    NS_DECL_NSIOBSERVER

  private:

    virtual ~DocumentLoadNotification() {}

    virtual void SetTo(Element* aTo) override { }

    nsString mRef;

  };

  friend class DocumentLoadNotification;

  DocumentOrShadowRoot* GetWatchDocOrShadowRoot() const

  {

    if (!mWatchDocumentOrShadowRoot) {

      return nullptr;

    }

    MOZ_ASSERT(mWatchDocumentOrShadowRoot->IsDocument() ||

               mWatchDocumentOrShadowRoot->IsShadowRoot());

    if (ShadowRoot* shadow = ShadowRoot::FromNode(*mWatchDocumentOrShadowRoot)) {

      return shadow;

    }

    return mWatchDocumentOrShadowRoot->AsDocument();

  }

  RefPtr<nsAtom> mWatchID;

  nsCOMPtr<nsINode> mWatchDocumentOrShadowRoot; // Always a `DocumentOrShadowRoot`.

  RefPtr<Element> mElement;

  RefPtr<Notification> mPendingNotification;

  bool mReferencingImage = false;

};

inline void

ImplCycleCollectionUnlink(IDTracker& aField)

{

  aField.Unlink();

}

inline void

ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,

                            IDTracker& aField,

                            const char* aName,

                            uint32_t aFlags = 0)

{

  aField.Traverse(&aCallback);

}

} // namespace dom

} // namespace mozilla

#endif /* mozilla_dom_IDTracker_h_ */